Chyna’s lawyer, Walter Mosley, tells TMZ … BC and Rob still have a valid custody agreement in place, and Chyna protecting her daughter shouldn’t affect it in any way. We’re told any attempts by Rob to alter custody stipulations will be defended “by any means necessary” … legally speaking.

Our Chyna sources say she stands by her claim she was simply doing what she had to do to protect her kids — both Dream and King Cairo — in the Six Flags incident … and doesn’t think her stroller swinging should be held against her.